Rafael Nadal arrived in Viña del Mar seeking to shake off the rust from his injury-induced seven-month absence from the sport. But as the copper-colored clay swirled around in Sunday's final, Nadal couldn't create separation from Horacio Zeballos and his dust-busting forehand.

Stepping into the court to smack his forehand with ambition, the 73rd-ranked Argentine delivered a stunning, 6-7 (2), 7-6 (6), 6-4 upset of the seven-time French Open champion to capture his first career ATP title and spoil the fifth-ranked Spaniard’s comeback tournament.

Nadal carried a 15-match clay-court winning streak and commanding 36-4 record in clay-court finals—only Roger Federer and Novak Djokovic had beaten Rafa at that stage—into the title match against Zeballos, who was contesting his second ATP tour-level final. All this, combined with the fact that Nadal had not surrendered a set in the tournament—and the reminder than he permitted just seven games to Zeballos in their lone prior meeting at the 2010 French Open—combined to create an atmosphere of impending coronation among fans, many of whom waved and wore the Spanish flag.

None of that mattered much to the 27-year-old underdog, who opened the year winning the Sao Paulo Challenger and looked poised playing the role of party crasher. Zeballos played boldly at crunch time, winning eight straight points to close an improbable victory.

The first ATP all-lefty final since the 2010 Monte Carlo Masters saw both men attack with their forehands throughout a tight opening set. Nadal opened a 5-1 lead in the first-set tiebreaker and struck an inside-out forehand winner for set point. Anticipating Zeballos’ wide serve, Nadal was off the doubles alley when he blasted a backhand return winner down the line to snatch the set with a fist-pumping flourish that brought the crowd to its feet.

Zeballos packs his pony-tail in a bun beneath his baseball cap, reminiscent of compatriot Gaston Gaudio, and unloads a sweeping swing on his forehand that recalls fellow Argentine left-handers Guillermo Vilas and Franco Squillari. Though Zeballos has 10 Challenger titles to his credit, consistency has been a challenge: He did not surpass the second round of an ATP event last year. Zeballos saved the only two break points in a second set that escalated into another tiebreaker.

Zeballos’ forcing forehand and a biting serve brought the Argentine to set point at 6-4 in the breaker. Then, after fending off a barrage of heavy forehands, Nadal short-circuited a crackling rally with an angled backhand drop shot. Grunting himself into gear, Zeballos ran it down, but flicked a full-stretch forehand out, then proceeded to press a ball against his temple like a man pained by a bruise—and worried into might swell into something much worse. When a backhand of sailed wide on the next point, it was six-all.

But this time, with Nadal serving, Zeballos sat on the backhand return and slammed his one-hander down the line—a master strike that recalled Rafa’s backhand return winner in the first set breaker. It earned Zeballos another set point, and this time he didn't blink. Opening the court with a punishing inside-out forehand, Zeballos waited for Nadal to make his move, then struck a sweeping forehand behind him to force a third set. It was the third tiebreaker Zeballos won this week—he beat Albert Ramos, 7-6 (6), in the third set of the quarterfinals, and defeated Carlos Berlocq, 6-3, 7-6 (4), in the semifinals.

When Nadal broke at love to open the third set, it appeared order had been restored. But the former No. 1 did not consistently produce the depth on his groundstrokes and paid the price. Nadal saved two break points in the very next game, but blocked a forehand drop volley into the top of the net to immediately drop serve.

A brilliant backhand stab volley from Nadal helped him erase a break point and gut out a hold for 4-4. But rather than rue that lost opportunity, Zeballos was strengthened by the struggle. He slammed an ace wide to hold at love for 5-4 and ratchet up the pressure on Nadal, who was drifting a bit too far behind the baseline in prevent-defense mode.

Zeballos exploited Nadal's court positioning with a forehand drop shot winner, then curled a gorgeous running forehand cross-court to shockingly earn triple match point. When Nadal found the net to end the two hour, 46-minute struggle, Zeballos fell flat on his back, collapsing to the court in a combination of exhilaration, relief, and disbelief. Some members of the crowd looked so astonished by the result that the initial reaction was a bit more muted than one might expect, but when Zeballos rose, his white Fila shirt caked in crushed red brick, the realization of the win struck all.

“It's a dream for me,” said Zeballos afterward. “To be able to play a final against Nadal was already good enough for me. It's a moment that will stay in my memory for the rest of my life.”

Zeballos never shook the clay that streaked his shirt or the smile plastered across his face, while Nadal must know the bulls-eye on his back grows larger after a stunning loss like this. Still, his game will grow sharper with each match.